The general packet radios system (GPRS) is a system that is used for transmitting Internet Protocol packets between user devices such as cellular phones and the Internet. The GPRS system includes the GPRS core network, which is an integrated part of the global system for mobile communication (GSM). These systems are widely utilized by cellular phone network providers to enable cellular phone services over large areas.
The GPRS tunneling protocol (GTP) is an important communication protocol utilized within the GPRS core network. GTP enables end user devices (e.g., cellular phones) in a GSM network to move from place to place while continuing to connect to the Internet. The end user devices are connected to the Internet through a gateway GPRS support node (GGSN). The GGSN tracks the end user device's data from the end user device's serving GPRS support node (SGSN) that is handling the session originating from the end user device.
Three forms of GTP are used by the GPRS core network. GTP-U is used for transfer of user data in separated tunnels for each packet data protocol (PDP) context. GTP-C is used within the GPRS core network for signaling between GGSN and SGSN. GTP′ is used for carrying charging data from Charging Data Function (CDP) of the GSM or UMTS network to the charging gateway function (CGF), which provides requisite end user device usage information to a billing system. GTP′ uses the same message structure as GTP-C and GTP-U.